This application addresses broad Challenge Area (15) Translational Science and specific Challenge Topic, 15-RR-101 Applied Translational Technology Development. The challenges of cancer diagnosis and prognosis call for sensitive, specific, and economical detector systems. Rapid advances in genomics and oncogenomics, in particular, are opening a period of great expansion in the range and effectiveness of DNA- and RNA-based diagnostics. These trends, which are expected to continue for the foreseeable future, call for transducers compatible with hybridization assays and molecular binding, implementable in parallel formats, with high sensitivity and specificity for target molecules. While current biomolecular recognition technologies can carry out genome-wide profiling of clinical specimens, they require relatively large samples, at the nanogram and microgram levels, which are often not readily available. Sample amplification is an option but can lead to erroneous results, especially where ratios of different analytes'concentrations can be skewed by differential amplification. There exists a critical need for novel technologies for ultra-small clinical specimen analysis, which will enable the use of precious, limited-amount samples such as formalin-fixed paraffin embedded tissues, sorted sub-populations or fine needle aspirate biopsy (FNAB) samples. The goal of the proposed work is to develop a single-molecule nanomagnetic array sensor that will enable efficient analysis of such clinical samples. The specific objective is to build a nanomagnetic sensor array capable of sensing single 50nm magnetic labels and to demonstrate high-sensitivity biomolecular diagnostic assays applicable to ultra-small clinical specimens such as FNAB or sorted cell sub-populations. The sensitivity of the device to low-abundance microRNAs, mRNAs or proteins is expected to be unprecedentedly high, potentially at the single-molecule level. The ability to base measurements on only one or a few probe and target molecules will improve the quality of the data by suppressing avidity effects arising from multiple interactions, and can reveal genuine single-molecule heterogeneity in target populations not detectable by population-averaged measurements. The rationale for this research is that such a nanomagnetic sensor can be based on rapidly-advancing magnetic hard disk data storage technology, and can be relatively easily integrated into a practical sensor array with an extremely high density of individually-addressable sensors. The impact of this research is that it will enable a new generation of biosensors capable of highly reliable and sensitive detection and characterization of mRNA, miRNA and protein biomarkers. The proposed research will advance biomagnetic sensing into a highly versatile clinical diagnostic technology, which will offer ultrasensitive (single-molecule) molecular detection and high specificity via magnetic field pull off melting to suppress non-specific associations. This research is expected to enable a new generation of highly reliable molecular diagnostic instrumentation with significantly enhanced sensitivity and high specificity.